Magnetic structure for speakers



Dec. 19, 1950 G. s. HOLLY 2,534,819

MAGNETIC STRUCTURE FOR SPEAKERS Filed Feb. 27, 1947 Patented Dec. 19, 1950 MAGNETIC STRUCTURE FOR SPEAKERS George S. Holly, Chicago, Ill., assignor, by mesne assignments, to Jensen Manufacturing Company, Chicago, Ill., a corporation of Nevada Application February 27, 1947, Serial No. 731,291

9 Claims.

This invention relates to a magnetic structure for speakers, and more particularly to a magnetic structure for speakers having a permanent magnet of very hard material.

It has been known that very hard materials, as for example aluminum-nickel alloys, have excellent permanent magnetic qualities and hence it is desirable to incorporate a permanent magnet of such alloys in a dynamic speaker. However, such metal is so hard that it cannot be satisfactorily drilled, tapped, machined or welded, and it has, therefore, been found very diificult to incorporate magnets of such very hard material in dynamic speakers.

This will be readily seen when it is considered that in order for the speaker to function properly the parts of the magnetic structure must be permanently secured together in an exactly correct relationship, and it is extremely difiicult to unite these members to accomplish the above results with the usual methods.

In my application for Speaker filed October 24, 1945, as Serial No. 624,134, now abandoned, I disclosed a novel and improved method of joining these parts together in the proper relationship and a new and useful product resulting from such method. I have now devised and am here disclosing a further improved method of making a magnetic structure for speakers having a permanent magnet of very hard material, and a new and useful product resulting therefrom. In particular my present invention results in the elimination of the pole piece which has conventionally been used in conjunction with the permanent magnet of very hard material used in such speakers, and I have devised a new means of securely fastening a magnet of very hard material to a frame, this means resulting in a simplified method of construction, and when the magnetic structure for speakers is manufactured in accordance with my invention a cheaper speaker (both as to part costs and assembly operations) results. In addition, my invention enables more compact construction because it saves depth in the magnetic structure of a speaker. This is particularly important in small speakers and small radio sets where space may be extremely limited.

Other features and advantages of my invention will be apparent from the following detailed description and from the drawings, in which:

Figure l is a side elevation of a speaker having a magnetic structure in accordance with my invention;

Figure 2 is a plan view of only the magnetic structure of the speaker illustrated in Figure 1;

Figure 3 is a section taken on the line 3--3 of Figure 2;

Figure 4 is an enlarged view of a modification of the structure shown in Figures 2 and 3;

Figure 5 is another modification of the structure shown in Figures 2 and 3;

Figure 6 is a section through a modified form of magnetic structure; and

Figure 7 is a section through another modified form of magnetic structure.

In Figure 1 the speaker comprises a diaphragm or cone l0 having a voice coil H. The cone may be carried in a rigid frame or basket I2, this basket being secured to a frame 13 in any conventional manner. As shown in the drawings the frame l3 comprises top and bottom portions, and in Figures 1 and 3 the bottom portion is illustrated as a fiat bottom member l3a and the top portion as a U-shaped yoke member l3b having an opening |3c through its body portion. A permanent magnet M of very hard material is securely fastened to the bottom portion [3a, and the voice coil 1 I surrounds this magnet, the mag: net being suificiently spaced from the walls of the opening |3c so that the voice coil may freely move with respect to the magnet.

In order to function properly, the parts of the magnetic structure of the speaker must be permanently secured together in exactly correct relationship, particularly the magnet must be in the exact center of the opening in the U-shaped member l3b, so that the voice coil which surrounds the neck of the speaker cone may have the same magnetic forces directed toward it at all times from the magnet and the frame.

The frame I3 is constructed of magnetic material, preferably although not necessarily cold rolled steel, and while said frame is designated in this application as having a top portion and a bottom portion, it will be understood that the designations top and bottom are utilized merely as a convenient means of designating the respective parts, for while said parts are shown in the drawings in top and bottom positions, it will be understood that the magnetic structure may be and often is utilized with these parts in some other position relative to each other.

The top and bottom portionsof the frame l3 may be secured together by-the solder l5, and this operation may be performedby placing two pieces of solder wire against the ends of the yoke and running the assembly through .an oven to melt the solder and join the parts together as more particularly disclosed in my copending application above referred to.

In constructing the apparatus shown in Figures 1, 2 and 3 the opening I30 in the top portion of the frame is circular and is co-axial with an opening Kid in the bottom portion of the frame, and the top opening l3c has a greater diameter than the bottom opening [311. As earlier stated, the permanent magnet I4 is preferably of very hard material, the term very hard being used in this specification to designate material which is too hard to be satisfactorily machined or welded, as for example an aluminum-nickel alloy. Consequently, all permanent magnets of such a very hard material used in speakers prior to this time have been cast and have been of such irregular dimensions that their use in speakers was prohibited unless such permanent magnet terminated short of the body portion of the U- shaped yoke part of the frame, and a, pole piece of steel or other material which can be machined to exact dimensions was afiixed to the permanent magnet so that a portion of this pole piece extended into the opening 130.

This was necessary because it is required for satisfactory operation that the magnet be exactly centered in the top opening in the frame with the periphery of the magnet equally spaced at all points from the wall of said opening. A. further difficulty was encountered in attempting to secure the very hard permanent magnet to the bottom of the frame, since such magnet could not be machined to exact specifications, and cast magnets were too irregular in shape to be accurately and securely mounted in an opening in the bottom of the frame.

I have discovered that permanent magnets of such a very hard material may be ground to exact specifications, and by centerless. grinding the permanent magnet I l I am able to form such magnet as a cylinder with a diameter equal to the diameter of the bottom opening !3d. The permanent magnet may then be securely fastened to the bottom portion of the frame by tightly press fitting said magnet into the opening i311.

Since the permanent magnet I 4 is ground to form a cylinder of exact specifications, it is no longer necessary to affix a pole piece to the magnet, but the magnet itself may extend into the top opening and be centered within said opening with its periphery equally spaced at all points from the walls of said opening. By inserting a plug of suitable material having a hollow end and having walls of substantially the same thickness as the space between the magnet and the walls of the opening E30 over the top of the magnet when it is pressed into the opening 13d the magnet will be properly centered within the opening I30.

In Figure 4 (in which numerals used are 20 higher than those used for similar parts in Figures l, 2 and 3) the frame 33 comprises a flat bottom member 33a having a portion 33a of increased thickness and an opening 33d through said portion. A U-shaped top member 332) hav ing through its body portion an opening 330 coaxial with, but of larger diameter than the opening 33d, is attached at its ends to the bottom member 3311 by means of the solder 35. A permanent magnet 3 of very hard material is tightly press fit into the opening 33d, said magnet extending into said top opening and being centered within the top opening in the manner heretofore described.

The provision of the portion 33a of increased thickness is particularly desirable in larger magnetic structures having very strong magnetic "fieldsassociated therewith, sinceisaid portion provides a larger gripping area on the magnet so that the magnet is more securely fastened to the frame, provides a better magnetic contact between the frame and the magnet (this being very advantageous when a very strong magnetic field is used), and allows a longer magnet to be used while increasing the over-all size of the structure only very little.

In Figure 5 the magnet 54 is mounted in the frame 53 in the same manner as shown in Figure 3, but the frame 53, while being substantially rectangular in vertical cross section as are the other frames illustrated, is of one piece construction, being formed in the shape of a hollow box and the ends of the one piece frame being joined together at 53e by soldering or other means. It will be readily seen that such a con struction is advantageous in manufacturing the frame and may be readily achieved since the openings 53c and 53d are coaxial and the permanent magnet 54 is adapted to be centered in the opening 530. Prior to my invention such a structure was not feasible since the magnet could not be accurately positioned in the bottom portion of the frame and could not be accurately centered in the opening 530.

in the modified form of my invention shown in Figure 6 (in which numerals used are 60 higher than those used for similar parts in Figures 1, 2 and 3) the frame '53 is a tubular element having a cylindrical portion 13d and side walls 'iiib flaring outwardly toward the top of the element. Magnet M- is tightly press fitted into the cylindrical portion of this frame'element as shown.

The basket "12 which supports the speaker cone has at least a portion made of magnetic material, and this portion has an opening 72a therethrough, this opening being of greater diameter than the diameter of the magnet 14. The frame it is secured to the basket 72 by any conventional means, as for example, by soldering, so that the magnet extends into the opening 12a, thus providing a very cheap but eflicient construction.

In Figure '7 frame 93 is again secured to the basket 92, and in this case the frame is again of U-shaped cross section but its sides are parallel to each other. A central opening 93d is in the bottom of the frame, and the space 930 between the side of the frame and the top portion of the magnet forms the required annular In making a magnetic structure in accordance with my inventions it is only necessary to first provide a frame of magnetic material having circular coaxial top and. bottom openings therethrough, said top opening having a greater diame'ter than said bottom opening. Since the frame may be made of a magnetic material which may be easily drilled or machined, as for example, cold rolled steel, these openings may be accurately provided whether the frame is of the construction shown in Figure 3 or is as shown in Figure 5. A permanent magnet of very hard material is then centerless ground to form a cylinder with a diameter equal to that of said bottom opening; and the magnet is then tightly press fitted into said bottom opening with a portion of the magnet extending into the top openthat if it is desired other means may be utilized to securely fasten the magnet to the bottom portion of the frame, as for example, the soldering means disclosed in my above mentioned copending application. In this event the bottom opening may be dispensed with, but the principles of the present invention are still applicable in forming the magnet to exact specifications so that it can be centered in the top opening.

It will also be obvious that if desired a pole piece may be utilized on the magnet, and the principles of this invention may be applied in securely fastening the magnet to the bottom portion of the frame accurately in a desired position.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. A magnetic structure for speakers comprising a cylindrical permanent magnet and a frame of magnetic material adapted to provide a magnetic circuit including said magnet, said frame comprising an open-ended tubular element of circular cross section coaxial with said magnet and having a cylindrical portion at one end thereof, said magnet having one end portion thereof held within the cylindrical portion of the tubular element by frictional engagement with the side walls thereof, said frame approaching but stopping short of the cylindrical surface of the magnet at the end thereof remote from that held by the cylindrical portion of said tubular element to form an annular air gap in the magnetic circuit.

2. A magnetic structure for speakers comprising a cylindrical permanent magnet and a frame of magnetic material adapted to provide a magnetic circuit including said magnet, said frame comprising an open-ended tube of circular cross section coaxial and coterminous with said magnet, the inside surface of said tube being uniformly spaced from said magnet throughout the length thereof except at one end of said magnet whereat the inside diameter of said tube is equal to the diameter of said magnet and said end of the magnet is securely held in intimate frictional engagement by said tube.

3. A magnetic structure for speakers comprising a frame of magnetic material comprising an open-ended tube of circular cross section, said tube having a cylindrical portion at one end thereof and flaring outwardly from said cylindrical portion toward the other end thereof, and a magnetic member engaging said tube at the end thereof remote from said cylindrical portion and having a circular opening therein concentric with said cylindrical portion of said tube, and a cylindrical permanent magnet, said magnet having one end portion thereof held within the cylindrical portion of the tube by frictional engagement with the side walls thereof, said magnet extending from said cylindrical portion through the outwardly-flaring portion of the tube and through said circular opening in concentric relation thereto.

4. A magnetic structure in accordance with claim 3 wherein the permanent magnet is composed of very hard material and the cylindrical surface thereof at the circular opening is smooth and exactly circular.

5. A ,magnetic structure in accordance with claim 4 in which the cylindrical surface of the magnet within the cylindrical portion of the tube is smooth and exactly circular.

6. A magnetic structure in accordance with claim 4 wherein the cylindrical magnet is of the same diameter throughout the length thereof.

7. In a speaker having a cone-supporting basket of magnetic material, a magnetic structure comprising an open-ended tube of circular cross section, said tube having a cylindrical portion at one end thereof and flaring outwardly from said cylindrical portion toward the other end thereof, the end of said tube remote from said cylindrical portion engaging said basket, said basket having a circular opening therein concentric with said cylindrical portion of said tube, and a cylindrical permanent magnet, said magnet having one end portion thereof frictionally engaging the inner surface of the side walls of the cylindrical portion of the tube and held therein, said magnet extending from said cylindrical portion through the outwardly-flaring portion of the tube and through said circular opening, in concentric relation thereto.

8. Structure in accordance with claim 7 wherein the permanent magnet is composed of very hard material and the cylindrical surface thereof at the circular opening is smooth and exactly circular.

9. A magnetic structure for speakers comprising a frame of magnetic material and comprising an open-ended tube of circular cross section, said tube having a cylindrical portion at one end thereof and flaring outwardly from said cylindrical portion toward the other end thereof, and a magnetic member engaging said tube at the end thereof remote from said cylindrical portion and having a circular opening therein concentric with and larger in diameter than the inside diameter of said cylindrical portion of said tube, and a cylindrical permanent magnet, said magnet having one end portion thereof held within the cylindrical portion of the tube by frictional engagement with the side walls thereof, said magnet extending from said cylindrical portion through the outwardly-flaring portion of the tube and through the circular opening in concentric relation thereto.

GEORGE S. HOLLY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,335,995 Cox Apr. 6, 1920 1,948,861 Sollie Feb. 20, 1934 2,020,212 Quam Nov. 25, 1935 2,029,282 serge Jan. 28, 1936 2,124,597 Tiedje July 26, 1938 2,138,461 Sundstrom Nov. 29, 1938 2,178,215 Anderson Oct. 31, 1939 2,207,064 Maurer, Jr. Jul 9, 1940 2,275,880 Arey Mar. 10, 1942 2,458,158 Gilman Jan. 4, 1949 FOREIGN PATENTS Number Country Date 200,119 Great Britain Oct. 19, 1933 403,778 Great Britain Jan. 4, 1934 Certificate of Correction Patent No. 2,534,819 December 19, 1950 GEORGE S. HOLLY It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 3 1, after the Word material strike out and;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 6th day of March, A. D. 1951.

[SEAL] THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

